Millions of dollars are spent each year in trying to improve a smile, align teeth and/or correct a periodontal defect. Tooth malocclusion and other periodontal defects are typically caused during periodontic development and by oral deformities, such as extra teeth and the like. Periodontic defects can lead to further problems if left uncorrected or unrepaired. For example, malocclused teeth may lead to problems associated with biting and the chewing of food as well as to problems related to jaw structure and jaw movement, and to the development of incoming permanent teeth. Accordingly, periodontic defects need to be corrected. In addition, young persons, particularly in their teens and twenties, are often unhappy with periodontic imperfections or problematic teeth, particularly if it affects their smile or appearance in general, and desire to have the problems corrected.
In the field of orthodontics, techniques to correct such problems include applying or attaching orthodontic appliances across the problematic areas, and in particular, across malocclused teeth to straighten or correct their alignments relative to each other and to the patient's skeletal structure. To this end, orthodontic appliances, such as brackets, buccal tubes and the like, are adhered directly to the surfaces of the teeth to transmit corrective forces from orthodontic archwires or other elastic devices to the teeth for corrective purposes. The orthodontic appliance that is most commonly attached to a tooth is the orthodontic bracket. The most common orthodontic bracket in use includes a rectangular slot to support an archwire and tie wings or other ligating structure for use in tying the archwire to the bracket. Such bracket structure is generally provided with a base or other tooth engaging structure with which the bracket is adhered to the tooth surface.
In orthodontics, the term ‘appliance’ may be used to refer to an entire assembly of components, including brackets, archwires, buccal tubes, etc., that are used to treat patients. The term ‘appliance’ may also be used to refer to the individual components of such assemblies, including the individual brackets and archwires, etc. Similarly, the term ‘bracket’ is used to refer to archwire supporting structure that usually contains an archwire slot and tie wings, which structure may be fixed to a bonding base, pad or other structure that supports the bracket on a tooth. The term ‘bracket’ may also apply to an entire device that includes the archwire supporting structure as well as bonding base structure to which the archwire supporting structure may be fixed.
More particularly, a bracket-type appliance generally has a bonding surface adapted to bond with adhesive to the surface of a patient's tooth. This surface may be a surface on the archwire support structure itself or may be a surface on a pad, which usually has a larger perimeter than the archwire support structure, and which is either formed integrally with the archwire support structure or as a separate sheet to which the archwire support structure of the bracket is fixed. Such a pad has the archwire support structure or bracket on one side thereof, the other side of the pad providing the bonding surface for bonding to a tooth. With either configuration, the bonding surface is referred to as a bonding base. The term ‘base’ in relation to a bracket is therefore used to refer to various parts of the structure between the archwire support and the adhesive that holds the bracket to a tooth.
The bonding surface to which adhesive is applied often includes structural elements, such as a mesh or other highly textured structure, that presents undercuts or other interlocking features and forms a mechanical or interlocking bond with adhesive that has filled the voids in the structure and hardened, thereby assisting in bonding the bracket to the tooth to which the adhesive is applied. Such a bonding surface is referred to as a ‘mechanical bonding base’. Adhesive is generally applied to a bonding surface of a tooth, with the orthodontic appliance being pressed onto the adhesive. The adhesive compound is then cured to create a chemical or mechanical bond between the adhesive and the tooth and a chemical and/or mechanical bond to the bonding base, pad, or other engaging structure on the bracket. In a similar fashion, each of a plurality of orthodontic appliances is adhered to the surface of a tooth and interconnected with each other by an archwire or otherwise to form the appliance.
In use, orthodontic appliances are subjected to a variety of forces exerted upon the appliance in addition to forces exerted on brackets by archwires. More particularly, force and energy are exerted against appliances when objects contact orthodontic appliances including brackets that are adhered to tooth surfaces. Such contacts result in forces that are conveyed or transferred through the bracket directly to the adhesive bond securing the appliance to the tooth. When the force exceeds the limitations of the adhesive bond, the bond may fracture, completely break, or totally fail resulting in the bracket being dislodged or debonded from the tooth. A rather small amount of contact may be all that is necessary to fracture the adhesive.
The loads that cause the debonding of orthodontic appliances from teeth most often come from the occlusal direction and are generally normal to the occlusal plane. Such loads that produce forces capable of causing the bond to crack or otherwise fail, and the appliance to thereby debond from the tooth surface, are typically exerted upon the appliance during normal, everyday activity. Mere eating and chewing of food, grinding of teeth, and other masticatory activity in the mouth may exert large forces on the appliance and, in particular, forces sufficient to cause the bracket adhesive to fail. Often it is the closing motion of the jaw that applies the forces against intervening hard objects against the teeth and appliances bonded to the teeth.
Orthodontists have experienced that a substantial percentage of brackets fail during treatment. The percentage may be in the area of about ten percent. With approximately two million orthodontic treatments being started each year in the United States, with each using typically twenty brackets per case, and with treatment lasting on the average about two years, a substantial number of failures, approximately forty million, may be expected to occur each year. With ten thousand practicing orthodontics in the United States, each orthodontist might expect, on average, four hundred failures per year. Estimating the cost to the orthodontist of each bracket failure at about seventy-five dollars, the loss, in time or money, to the average orthodontist may be calculated at about $30,000. Accordingly, bracket failure is a major problem that must be addressed.
To address the problems of the failures of adhesives between orthodontic appliances and teeth, the prior art has focused on the forces involved in bond failure. Such forces are traditionally analyzed by tests designed to measure static loads on the appliance. To resist these forces and to prevent dislodging of the orthodontic appliance from the tooth, the prior art has focused on strengthening the bond between the appliance and the tooth.
For example, U.S. Pat. No. 5,071,344 to Wong teaches an orthodontic appliance having a bracket with a base portion for attachment to the tooth. The base portion has a substantial monolayer formed of substantially uniform size particles. The particles provide a larger contact surface for bonding to the adhesive to generate a stronger bond.
U.S. Pat. No. 5,110,290 to Wong teaches an orthodontic appliance having a ceramic engaging surface for attachment to the tooth. This patent discloses the use of a wire mesh between the ceramic engagement surface of the base portion of the appliance and points of attachment on the tooth. The wire mesh has a plurality of openings through which the adhesive passes to allow for a stronger mechanical bond between the adhesive and the mesh.
U.S. Pat. No. 5,722,826 to Tuneberg teaches a bonding pad for an orthodontic attachment to be bonded to a tooth, including a foil or plate having a photoetched surface, and a layer of mesh material diffusion bonded to the photoetched surface. The photoetched surface provides a secondary bond interlock, while the mesh provides a primary bond interlock, thereby increasing the strength of the bond between the bonding pad attached to a bracket and the tooth.
While prior art orthodontic appliances have improved the bonding strength between the orthodontic appliance and the tooth, such improvements are not without their drawbacks. For instance, stronger bonds can concentrate impacts and forces and potentially lead to fracture of the adhesive and/or the bracket-base, and thereby dislodge the appliance. Further, stronger, more secured mechanical bonds between the bracket and the mesh generally concentrate this force to specific locations or points in the adhesive. This concentration of force leads to a greater likelihood of bond failure and dislodging or even debonding of the appliance upon smaller, less energetic contacts or impacts. In effect, some of the increased force resistance provided by the stronger bond is countered by the concentration of the impacting force.
Further, strengthening the bond can have deleterious effects. With a stronger bond between the bracket and the tooth, if the bracket dislodges upon impact, it is more likely to remain bound to the adhesive layer thereby dislodging or tearing with it a portion of the underlying enamel from the surface of the tooth. Further, a stronger bond renders the appliance more difficult for an orthodontic practitioner to remove without adverse effects up to and including the pulling of tooth enamel from the tooth. Torn enamel not only causes pain to the patient, but also requires a repair which is both inconvenient and costly.
Consequently, the prior art has also attempted to develop orthodontic appliances designed to reduce such tearing and pulling of tooth enamel when they are debonded. U.S. Pat. No. 5,263,859 to Kesling teaches an improved, flexible bonding pad or base for an orthodontic ceramic bracket to facilitate debonding of the bracket from the tooth and a method of debonding. This base or pad is formed of relatively flexible material to allow the application of compressive and buckling force, with dental pliers, to break the bond between the base and the tooth for removal of the bracket therefrom. Removal of the bracket is accomplished without subjecting the bracket to such forces capable of fracturing the bracket.
U.S. Pat. No. 6,017,216 to Deleo, teaches an orthodontic bracket apparatus, for attachment to a tooth, consisting of a flexible attachment pad having a pair of brackets permanently mounted on adjoining areas at one side of the pad and spaced in relation to each other. This side-by-side arrangement of the brackets is intended to provide easy arcuate adjusting movement of each bracket with respect to the other bracket so as to obtain a tighter fit of the entire pad to the surface contours of the tooth to which the apparatus is affixed.
While the prior art has proposed solutions which strengthen the chemical or mechanical bond adhering the orthodontic appliance to the tooth surface, these methods, however, have done so at the expense of making the appliance more difficult to remove once the teeth have been corrected, and increase the risk of tearing and removing a portion of the enamel of a tooth when the appliance is removed by the orthodontic practitioner or when it is unintentionally debonded due to impact. Consequently, the person wearing the orthodontic appliance faces additional problems, such as added cost, repair and inconvenience.
Thus, there is a need to provide an orthodontic bracket or other appliance for attachment to a tooth that will resist commonly encountered events during normal masticatory activity and removal practices without having the undesirable side effects and drawbacks of the prior art orthodontic appliances discussed above.